We numerically investigate the main constrains for high efficiency wavelength conversion of differential phase-shift keying (DPSK) signals based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF). Using multi-tone pump phase modulation techniques, high efficiency wavelength conversion of DPSK signals is achieved with the stimulated Brillouin scattering (SBS) effects effectively suppressed. Our analysis shows that there is a compromise between conversion efficiency and converted idler degradation. By optimizing the pump phase modulation configuration, the converted DPSK idler's degradation can be dramatically decreased through balancing SBS suppression and pump phase modulation degradation. Our simulation results also show that these multi-tone pump phase modulation techniques are more appropriate for the future high bit rate systems.
Schemes integrating inter-carrier interference(ICI) self-cancellation and common phase error(CPE) compensation for coherent optical orthogonal frequency division multiplexing(CO-OFDM) systems are investigated.The purpose of our research is to counteract the impacts of laser phase noise and fiber nonlinearity.We propose two ICI self-cancellation-based CO-OFDM schemes,and adopt a pilot-aided decision feedback(DFB) loop for CPE compensation.The proposed schemes are compared with conventional CO-OFDM schemes at the same spectral efficiency.Simulations show that our schemes can not only enhance laser linewidth tolerance of the CO-OFDM system,but also present strong robustness against fiber nonlinearity.
A novel scheme for ultra-wideband(UWB) monocycle pulse generation is proposed based on a dual-output push-pull Mach-Zehnder modulator(MZM).The MZM is driven by a non-return-to-zero(NRZ) data sequence and biased at the nonlinear point to generate edge-triggered pulses.To combine the complementary pulses forming a monocycle UWB pulse,two schemes are used to implement incoherent summation structure. A proof-of-concept experiment of UWB-over-fiber down-link system is set up.Further,by using digital signal processing(DSP) to calculate the bit error rate(BER),the transmission performance of two system configurations is studied.
Orthogonal frequency division multiplexing-passive optical network (OFDM-PON) and single-carrier fre-quency division multiplexing (SCFDM)-PON are promising solutions for future high-speed PON-based access. A polarization division multiplexing scheme with direct detection is proposed for OFDM-PON to effectively reduce bandwidth requirements for components. However, the scheme strictly requires spec-trum overlapping of two orthogonal sidebands and the 4×4 multi-input-multi-output (MIMO) algorithm to eliminate complex cross-polarization interference. In this letter, we propose a polarization interleaving (PI) approach that significantly reduces bandwidth requirements for optical and electrical components while achieving a high-flexibility and low-complexity MIMO algorithm. Downstream single sideband PI-SCFDM transmission is experimentally demonstrated.
